全文获取类型
收费全文 | 315587篇 |
免费 | 3789篇 |
国内免费 | 1094篇 |
专业分类
化学 | 171482篇 |
晶体学 | 4464篇 |
力学 | 13045篇 |
综合类 | 7篇 |
数学 | 36385篇 |
物理学 | 95087篇 |
出版年
2020年 | 1992篇 |
2019年 | 1963篇 |
2018年 | 1970篇 |
2017年 | 1882篇 |
2016年 | 3878篇 |
2015年 | 3263篇 |
2014年 | 4447篇 |
2013年 | 14008篇 |
2012年 | 10760篇 |
2011年 | 13395篇 |
2010年 | 8313篇 |
2009年 | 8281篇 |
2008年 | 12366篇 |
2007年 | 12608篇 |
2006年 | 12251篇 |
2005年 | 11185篇 |
2004年 | 10076篇 |
2003年 | 8887篇 |
2002年 | 8744篇 |
2001年 | 10150篇 |
2000年 | 7747篇 |
1999年 | 6133篇 |
1998年 | 4918篇 |
1997年 | 4750篇 |
1996年 | 4792篇 |
1995年 | 4387篇 |
1994年 | 4134篇 |
1993年 | 3979篇 |
1992年 | 4464篇 |
1991年 | 4315篇 |
1990年 | 4026篇 |
1989年 | 3845篇 |
1988年 | 4136篇 |
1987年 | 3809篇 |
1986年 | 3699篇 |
1985年 | 5341篇 |
1984年 | 5413篇 |
1983年 | 4393篇 |
1982年 | 4772篇 |
1981年 | 4806篇 |
1980年 | 4557篇 |
1979年 | 4675篇 |
1978年 | 4683篇 |
1977年 | 4663篇 |
1976年 | 4612篇 |
1975年 | 4521篇 |
1974年 | 4374篇 |
1973年 | 4537篇 |
1972年 | 2583篇 |
1971年 | 1889篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
851.
Summary We have recently reported on a new scaling theory of the rupture of colloid aggregates. The scaling theory is compared with
a simulation study of the transient response of sheared 2d aggregates. In this paper we discuss the origins of deviations from the predicted scaling behaviour. We also report some
of the steady-state configurations formed post rupture.
Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994. 相似文献
852.
Inversion of a triangular matrix can be accomplished in severalways. The standard methods are characterized by the loop ordering,whether matrix-vector multiplication, solution of a triangularsystem, or a rank-1 update is done inside the outer loop, andwhether the method is blocked or unblocked. The numerical stabilityproperties of these methods are investigated. It is shown thatunblocked methods satisfy pleasing bounds on the left or rightresidual. However, for one of the block methods it is necessaryto convert a matrix multiplication into the solution of a multipleright-hand side triangular system in order to have an acceptableresidual bound. The inversion of a full matrix given a factorizationPA=LU is also considered, including the special cases of symmetricindefinite and symmetric positive definite matrices. Three popularmethods are shown to possess satisfactory residual bounds, subjectto a certain requirement on the implementation, and an attractivenew method is described. This work was motivated by the questionof what inversion methods should be used in LAPACK. 相似文献
853.
The recently proposed Harbola–Sahni local potential in its exchange-only version [Phys. Rev. Lett. 62 , 689 (1989)] is found to give the static dipole and quadrupole polarizabilities for the Neisoelectronic series in excellent agreement with the corresponding Hartree–Fock estimates. © 1992 John Wiley & Sons, Inc. 相似文献
854.
Long-Mei Zeng Xiong Fu Jing-Yu Su Florecita De Guzman J. Francis Schmitz M. Bilayet Hossain Dick van Der Helm 《中国化学》1991,9(2):136-143
Three pyrrololactam alkaloids have been isolated from the marine sponge Phacellia fusca Schmidt collected from the South China Sea, and their structures were determined as 1–3 , on the grounds of spectral data. This is the first report of these compounds from this sponge. The structure of 1 was confirmed by X-ray analysis. 相似文献
855.
In [1, 2] we established and dicussed the algebra of observables for 2+1 gravity at both the classical and quantum level. Here our treatment broadens and extends previous results to any genusg with a systematic discussion of the centre of the algebra. The reduction of the number of independent observables to 6g-6(g>1) is treated in detail with a precise classification forg=1 andg=2. 相似文献
856.
N. M. Agababyan M. R. Atayan M. Charlet J. Czyżewski E. A. De Wolf K. Dziunikowska A. M. F. Endler Z. Sh. Garutchava H. R. Gulkanyan R. Sh. Hakobyan J. K. Karamyan D. Kisielewska W. Kittel S. S. Mehrabyan Z. V. Metreveli E. C. Oliveira K. Olkiewicz F. K. Rizatdinova E. K. Shabalina L. N. Smirnova M. D. Tabidze L. A. Tikhonova A. V. Tkabladze A. G. Tomaradze F. Verbeure S. A. Zotkin 《Zeitschrift fur Physik C Particles and Fields》1996,71(1):405-414
The NA22 data onπ ? π ? correlations are analyzed in terms of a number of two- and three-dimensional parametrizations (Gaussian space-time, Goldhaber, Bowler string-like, Bertsch hydrodynamical, Kopylov-Podgoretskii, etc.). Contrary to the results obtained for e+e? andµp collisions, the Goldhaber parametrization, as well as string-like models, fail in describing the hadron-hadron data. Better fits are obtained in the framework of surface-emitting fireball-like models, both when including and excluding hydrodynamical expansion of nuclear matter. Our results indicate that pion radiation occurs at earlier stages of matter evolution than in nuclear collisions. 相似文献
857.
Jadwiga Frelek Günther Snatzke Wojciech J. Szczepek 《Fresenius' Journal of Analytical Chemistry》1993,345(11):683-687
Summary Bidentate complexes of dimolybdenum tetraacetate with 1,3-diaxial diols show Cotton effects around 490–540 nm (CD band I), 400–440 nm (II), 350–380 nm (III), 320 nm (IV) and 280 nm (V). The sign of the Cotton effect II can be predicted by a proposed sector rule. It seems that from the Cotton effects for cyclic 1,3-diols the absolute configurations or conformations can be obtained.A part of this material was presented at III-rd International Conference on CD Spectroscopy [1] 相似文献
858.
A rooted graph is a pair (G,x), where G is a simple undirected graph and x ∈ V(G). If G is rooted at x, its kth rotation number hk (G,x) is the minimum number of edges in a graph F of order |G| + k such that for every v ∈ V(F) we can find a copy of G in F with the root vertex x at v. When k = 0, this definition reduces to that of the rotation number h(G,x), which was introduced in [“On Rotation Numbers for Complete Bipartite Graphs,” University of Victoria, Department of Mathematics Report No. DM-186-IR (1979)] by E.J. Cockayne and P.J. Lorimer and subsequently calculated for complete multipartite graphs. In this paper, we estimate the kth rotation number for complete bipartite graphs G with root x in the larger vertex class, thereby generalizing results of B. Bollobás and E.J. Cockayne [“More Rotation Numbers for Complete Bipartite Graphs,” Journal of Graph Theory, Vol. 6 (1982), pp. 403–411], J. Haviland [“Cliques and Independent Sets,” Ph. D. thesis, University of Cambridge (1989)], and J. Haviland and A. Thomason [“Rotation Numbers for Complete Bipartite Graphs,” Journal of Graph Theory, Vol. 16 (1992), pp. 61–71]. © 1993 John Wiley & Sons, Inc. 相似文献
859.
An FFT method is described for the solution of Poisson's equationover a rectangular region with Robbins boundary conditions oneither one or two sides of the region, together with suitableconditions on the rest of the boundary. In contrast to earlierapplications of the FFT technique, the equations for the Fourierharmonic amplitudes do not decouple into simpler independentsystems and an effective iterative scheme is developed for thesolution of these equations. A theoretical convergence analysisis shown generally to support the results obtained from practicalcomputation. For the test problems considered the method isfound to take between 3 and 4 times the execution time for problemssoluble directly by the FFT technique. 相似文献
860.
D. Kaptás T. Kemény J. Balogh L. F. Kiss L. Gránásy I. Vincze 《Hyperfine Interactions》1994,94(1):1861-1865
The temperature dependence of the iron hyperfine field distribution is reported in melt-quenched amorphous Fe-Zr alloys. The most remarkable feature is the compositinal change in the shape of the average hyperfine field versus temperature curves. The unusual increase in the average hyperfine field below about 85 K is a characteristic feature of the RSG systems; however, no anomaly is observed in the width of the hyperfine field distribution as a function of temperature. The results cannot be properly explained in the framework of the existing spin glass models. 相似文献